---
title: "Unloading AMSI via Reflection"
excerpt: "Impair Defenses
, PowerShell
, Command and Scripting Interpreter
"
categories:
  - Endpoint
last_modified_at: 2021-06-09
toc: true
toc_label: ""
tags:
  - Impair Defenses
  - PowerShell
  - Command and Scripting Interpreter
  - Defense Evasion
  - Execution
  - Execution
  - Splunk Enterprise
  - Splunk Enterprise Security
  - Splunk Cloud
---



[Try in Splunk Security Cloud](https://www.splunk.com/en_us/products/cyber-security.html){: .btn .btn--success}

#### Description

The following analytic utilizes PowerShell Script Block Logging (EventCode=4104) to identify suspicious PowerShell execution. Script Block Logging captures the command sent to PowerShell, the full command to be executed. Upon enabling, logs will output to Windows event logs. Dependent upon volume, enable on critical endpoints or all. \
This analytic identifies the behavior of AMSI being tampered with. Implemented natively in many frameworks, the command will look similar to `SEtValuE($Null,(New-OBJEct COLlECtionS.GenerIC.HAshSEt{[StrINg]))}$ReF=[ReF].AsSeMbLY.GeTTyPe("System.Management.Automation.Amsi"+"Utils")` taken from Powershell-Empire. \
During triage, review parallel processes using an EDR product or 4688 events. It will be important to understand the timeline of events around this activity. Review the entire logged PowerShell script block.

- **Type**: [TTP](https://github.com/splunk/security_content/wiki/Detection-Analytic-Types)
- **Product**: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

- **Last Updated**: 2021-06-09
- **Author**: Michael Haag, Splunk
- **ID**: a21e3484-c94d-11eb-b55b-acde48001122


#### Annotations

<details>
  <summary>ATT&CK</summary>

<div markdown="1">


| ID             | Technique        |  Tactic             |
| -------------- | ---------------- |-------------------- |
| [T1562](https://attack.mitre.org/techniques/T1562/) | Impair Defenses | Defense Evasion |

| [T1059.001](https://attack.mitre.org/techniques/T1059/001/) | PowerShell | Execution |

| [T1059](https://attack.mitre.org/techniques/T1059/) | Command and Scripting Interpreter | Execution |

</div>
</details>


<details>
  <summary>Kill Chain Phase</summary>

<div markdown="1">

* Exploitation


</div>
</details>


<details>
  <summary>NIST</summary>

<div markdown="1">



</div>
</details>

<details>
  <summary>CIS20</summary>

<div markdown="1">



</div>
</details>

<details>
  <summary>CVE</summary>

<div markdown="1">


</div>
</details>

#### Search 

```
`powershell` EventCode=4104 ScriptBlockText = *system.management.automation.amsi* 
| stats count min(_time) as firstTime max(_time) as lastTime by EventCode ScriptBlockText Computer user_id 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `unloading_amsi_via_reflection_filter`
```

#### Macros
The SPL above uses the following Macros:
* [security_content_ctime](https://github.com/splunk/security_content/blob/develop/macros/security_content_ctime.yml)
* [powershell](https://github.com/splunk/security_content/blob/develop/macros/powershell.yml)

> :information_source:
> **unloading_amsi_via_reflection_filter** is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

#### Required field
* _time
* Message
* OpCode
* ComputerName
* User
* EventCode


#### How To Implement
To successfully implement this analytic, you will need to enable PowerShell Script Block Logging on some or all endpoints. Additional setup here https://docs.splunk.com/Documentation/UBA/5.0.4.1/GetDataIn/AddPowerShell#Configure_module_logging_for_PowerShell.

#### Known False Positives
Potential for some third party applications to disable AMSI upon invocation. Filter as needed.

#### Associated Analytic story
* [Hermetic Wiper](/stories/hermetic_wiper)
* [Malicious PowerShell](/stories/malicious_powershell)




#### RBA

| Risk Score  | Impact      | Confidence   | Message      |
| ----------- | ----------- |--------------|--------------|
| 49.0 | 70 | 70 | Possible AMSI Unloading via Reflection using PowerShell on $ComputerName$ |


> :information_source:
> The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author. 

#### Reference

* [https://docs.splunk.com/Documentation/UBA/5.0.4.1/GetDataIn/AddPowerShell#Configure_module_logging_for_PowerShell.](https://docs.splunk.com/Documentation/UBA/5.0.4.1/GetDataIn/AddPowerShell#Configure_module_logging_for_PowerShell.)
* [https://blog.palantir.com/tampering-with-windows-event-tracing-background-offense-and-defense-4be7ac62ac63](https://blog.palantir.com/tampering-with-windows-event-tracing-background-offense-and-defense-4be7ac62ac63)
* [https://static1.squarespace.com/static/552092d5e4b0661088167e5c/t/59c1814829f18782e24f1fe2/1505853768977/Windows+PowerShell+Logging+Cheat+Sheet+ver+Sept+2017+v2.1.pdf](https://static1.squarespace.com/static/552092d5e4b0661088167e5c/t/59c1814829f18782e24f1fe2/1505853768977/Windows+PowerShell+Logging+Cheat+Sheet+ver+Sept+2017+v2.1.pdf)
* [https://www.crowdstrike.com/blog/investigating-powershell-command-and-script-logging/](https://www.crowdstrike.com/blog/investigating-powershell-command-and-script-logging/)



#### Test Dataset
Replay any dataset to Splunk Enterprise by using our [replay.py](https://github.com/splunk/attack_data#using-replaypy) tool or the [UI](https://github.com/splunk/attack_data#using-ui).
Alternatively you can replay a dataset into a [Splunk Attack Range](https://github.com/splunk/attack_range#replay-dumps-into-attack-range-splunk-server)


* [https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1059.001/powershell_script_block_logging/windows-powershell-xml.log](https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1059.001/powershell_script_block_logging/windows-powershell-xml.log)



[*source*](https://github.com/splunk/security_content/tree/develop/detections/endpoint/unloading_amsi_via_reflection.yml) \| *version*: **1**